Ian Cowie was named Consumer Affairs Journalist of the Year in the
London Press Club Awards 2012. He has been head of personal finance at
Telegraph Media Group since 2008, having been personal finance editor
since 1989. He joined the paper in 1986. He is @iancowie on Twitter.

It’s also good news for anyone who fears they may have missed the boat after a sharp spike in the retail prices index (RPI) reported this week. NS&I spokesman Gill Stephens told me: “If you buy Index-linked certificates in May, the starting point for your investment will be the RPI index level in March.

“The reason is that those investors who bough early in May would have done so before the April RPI figures – showing inflation rising at 5.3 per cent per annum – were announced this week. So, for the whole of May, buyers of Index-linked get the March RPI figure – when inflation was rising at 4.4 per cent.”

While the figures may seem small, the fact is that the annual rate of inflation jumped by 20 per cent between March and April. I suspect that NS&I’s reluctance to change its inflation starting points during the month dates back to Index-linked certificates’ pre-digital origins, when paper-based records would have made swifter updating difficult.

Whatever the reason, this gem in the small print is a rare example of a financial institution giving investors the benefit of the doubt. But Index-linked certificates are three and five year fixed term investments and it is also important to beware that the advertised return of RPI plus 1 per cent tax-free is only paid to investors who hold to maturity. Lower interest rates are paid on early redemption. If you want to see how returns accumulate over the years, click here.